1. Field of the Invention
The invention relates to the field of metallic reflective filler-containing coatings, particularly such coatings as are applied to roofing and other surfaces to impart solar reflectance.
2. Description of Related Art
Aluminum and other reflective coatings are known for use in roofing and other applications as a way to impart solar reflectance to structures to which they are applied. This results in protection of the underlying surface as well as energy savings that stem from reduced building cooling costs in hot climates. Solar reflectance is the measure of the fraction of incident solar energy that is reflected by a given surface. One way this is measured in the art is that different roof surfaces and roof coatings have different Solar Reflectance Indices (SRI). The SRI measures a roofs ability to reject solar heat demonstrated by temperature rise. Standard black roofing, which would have a solar reflectance of about 0.05 (and an emittance of about 0.90) has an SRI of 0 while a standard white roof having a reflectance of about 0.80 (and an emittance of about 0.90) has an SRI of 100. Standard black roofing has a temperature rise of about 90° F. (50° C.) when fully exposed to the sun, and standard white roofing would have a temperature rise of only about 14-15° F. (about 8° C.). The SRI of a material is calculated by interpolating its temperature rise between the values for white and black roofing. Materials having high SRI values are those which demonstrate cool roofing selections.
Traditional reflective coatings comprise aluminum and are formulated so as to maximize solar reflectance properties as a function of total aluminum pigment in the formulation. Attempts are made to achieve the highest possible solar reflectance value at the lowest possible use of aluminum pigment so as to minimize cost of the resulting coatings and products to which they are applied.
Other challenges in the art of forming such coatings are to minimize hard-packed settling which occurs in the container in which the coating is packaged. This hard-packed condition can further deteriorate the longer the container is held in storage prior to use and further promoted when the container is stored in hot and/or non-temperature controlled warehousing conditions. This problem causes the applicator to severely struggle in stirring the coating to uniformity in the container prior to applying the coating to a surface. Prior solutions to reducing hard-packed settling properties in such coatings include use of surface active agents, thixotropic agents, and other rheological modifiers that may aid in preventing hard packed settling in the product container. These traditional approaches have the detrimental effect of reducing or inhibiting solar reflectance properties of the dried coating thereby causing less efficient use of the high cost aluminum pigment.
Prior art attempts in improving solar reflectance properties to counteract the negative affect to settling associated with traditional anti-settling concepts in such coatings have met with varying success and/or have imparted unwanted additional cost to the overall formulation, and in the case of using additional solvents, have contributed to increasing the coatings volatile organic compound (VOC) load.